WASHINGTON -- U.S. Secretary of State John Kerry says that Washington remains at odds with Russia and Iran over Syrian President Bashar al-Assad’s future as part of a possible deal to bring an end to the civil war in Syria.

Kerry said in a November 12 speech that neither peace nor the defeat of the extremist Islamic State (IS) group is possible if Assad remains in power, and “without a real transition,” the 4-year-old war “will never end.”

“We are still working through with Russia and Iran the question of Assad and his role,” Kerry said. “It has not been settled. We acknowledge that. But...we and our partners believe that we can find a road ahead.”

Kerry’s speech at the U.S. Institute Of Peace, a Washington-based think tank, came ahead of a fresh round of Syria peace talks in Vienna on November 14 that will include 17 countries and three international bodies.

Both Iran and Russia have stepped up their support for Assad, with Moscow backing his forces in their battle against both IS and other Islamist militants as well as moderate Syrian opposition groups.

The Kremlin says Assad’s military represents the most capable force for defeating IS militants, while Washington and its allies accuse Assad of targeting his own population in the civil war, thus making his role in a postwar government untenable.